In X-ray based imaging systems, an X-ray source typically emits radiation (i.e., X-rays) towards a subject or object, such as a patient or luggage to be imaged. Hereinafter, the terms “subject” and “object” may be interchangeably used to describe anything capable of being imaged. The X-ray beams, after being attenuated by the subject or object, typically impinge upon an array of radiation detector elements of a detector that generates readable signals in response to the impinging radiation. The intensity of radiation beams reaching the detector is typically dependent on the attenuation and absorption of X-rays through the scanned subject or object. In certain detectors, a scintillator converts the X-ray radiation to lower energy optical photons that strike the detector elements. Each of the detector elements then produces a separate electrical signal indicative of the amount of X-ray radiation at the particular location of the element. The electrical signals are collected, digitized and transmitted to a data processing system for analysis and further processing to reconstruct an image.
As the image is reconstructed based on the electrical signals transmitted which are generated based on the amount of optical photons emitted by the scintillator, the performance of the detector system is affected by the scintillator's conversion of radiation to optical photons. Specifically, the quantum efficiency of the detector, or the sensitivity of the detector to the photons emitted by the scintillator, affects the accuracy of the detector in generating electrical signals indicative of the detected optical photons.
Conventionally, scintillator-based detectors are fabricated directly onto an array of pixel elements (e.g., TFT array). For example, layers of the detector may be deposited (e.g., spin coated, spray coated, etc.) on the TFT array, and a metal cathode may be used to electrically connect the detector to the scintillator. However, in the resulting configuration the photodetector may have a decreased quantum efficiency (e.g., by approximately 20%), due to photon absorption by the cathode. Such decreases in quantum efficiency of the detector may result in inefficiencies in the radiation detector system and/or inaccuracies in the reconstructed image.